[sdiy] protection circuit at audio output

[Antti PitkXmXki]

Hi!

I've lately been using my old Commodore 64 computer for making music. I dig 
the sound of its Sound Interface Device (SID)-chip. I'm planning to build a 
special cable for connecting the SID's audio output to my mixer. However, 
I've heard that the SID can possibly be killed by turning off the mixer 
where it is connected. This might be because of a voltage spike. A solution 
would be to always to unplug the C64's audio output from the mixer before 
turning the mixer off, but a mistake would happen sooner or later. So what 
should be done is to build a protection circuit to prevent any voltage 
spikes at the SID's output from killing it. One schematic I saw had two 
antiparallel diodes between the signal and the ground, plus a series 
resistor (470 ohms). The problem with this solution IMO is that the diodes 
were silicon diodes that limit the voltage between +/-0,7V, and I read 
somewhere that SID's maximum output is 2 volts peak to peak... So with that 
circuit I'd possibly get distortion.

Since I think it's possible that some of you synth-DIY-gurus have had to 
build a protection circuit to an audio output, I was wondering if you could 
provide me with suggestions for a protection circuit for my C64's SID? I 
guess a capacitor could be used to "filter" possible evil voltage spikes, 
but the idea is that it shouldn't affect the SID's sound in any way, and I 
don't have enough skill to choose the right parts.

Antti P.

PS: Really great year 2007 to everybody! :)

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